1. FIELD OF THE INVENTION
The invention relates to continuously variable transmission mechanisms which are of the kind comprising a variator with input and output sheaves of variable diameters and a flexible band connecting the sheaves together, an epicyclic gearset incorporated in the mechanism, and clutches and/or brakes arranged for selectively coupling together or selectively holding stationary various parts of the mechanism to provide forward and reverse transmission ranges within which the over-all transmission ratio can be varied by the variator.
2. DESCRIPTION OF THE PRIOR ART
Transmission mechanisms of this kind are known, for example from U.K. Patent Specification No. 1,128,694. Particularly when such a transmission mechanism is to be used in a commercial vechicle, it is desirable to provide a wide spread of gear ratios between the lowest (highest reduction) ratio and the highest ratio of the transmission. In contrast to this, in the interests of high efficiency and low stresses on the variator, it is desirble to limit the range of variator transmission ratios to a much lower range than is required by the vehicle. The provision of an epicyclic gearset such as is provided in the known transmission mechanism, can be used to enable the transmission mechanism to operate in various modes, thus extending the range of ratios of the overall transmission beyond that of the variator itself to provide a suitable range of overall transmission ratios. It is also desirable in the interests of efficiency that the variator should not have to operate for long periods of time with a high step-up or reduction ratio, particularly when a large amount of power is being transmitted. The known transmission referred to above circulates power within the transmission resulting in a large power transmission through the variator. Also, if used in a road vehicle, the known transmission mechanism would operate with a high step-up sheave ratio and a large power throughput when the vehicle travels at high speed.